48 



Illinois Natural History Survey Bulletin 



Vol. 23, Art. 1 



males produced during the colder months 

 are all wingless. Examination of pupae 

 shows that in these brachypterous females 

 the wings are abortive even in the pupal 

 stage. Winged females have been taken only 

 during the warmer months of the year. No 



Fig. 172. — Trentonius distinctus, male geni- 

 talic parts, showing variation. A, claspers; 

 B, tenth tergite, dorsal aspect; C, tenth tergite, 

 lateral aspect. 



intergradations between the normally winged 

 specimens and practically wingless specimens 

 have been observed. It would seem from 

 this that these two conditions of the wings 

 are probably caused by a temperature reac- 

 tion influencing the late larvae, similar in 

 behavior to certain characters observed in 

 genetic studies of Drosophila. There is con- 

 siderable variation in the relative propor- 

 tions of the claspers in this species, appar- 

 ently correlated to a large degree with size 

 of individual: large individuals have the 

 claspers very wide; smaller specimens have 

 them much narrowed, fig. 172. As a gen- 

 eral rule, the larger specimens of the males 

 occur during the colder months of the year, 

 so there is also an apparent correlation be- 

 tween width of clasper and seasonal appear- 

 ance. 



Chimarra Stephens 



Chimarra Stephens (1829, p. 318). Geno- 

 type, monobasic: Phryganea marginata Lin- 

 naeus. 



Chimarrha Burmeister (1839) and many 

 other authors, an emendation. 



Four species of this genus occur in Illi- 

 nois and a fifth may be taken in future col- 

 lecting. The larvae and adults of all our 

 species are identical in external appearance, 

 differing in the characters mentioned in the 

 key. 



Larvae. — Length 11-12 mm. Head and 

 pronotum golden brown, legs and anal hooks 

 straw colored. Body whitish with two or 

 three pairs of fine setae on each segment. 

 Legs having short claws with a short tooth 

 at base; anal hooks small and without inner 

 teeth. 



Adults. — Length 6-8 mm. Color dark 

 brown, almost black, the sides of the ab- 

 domen and sometimes portions of the femora 

 creamy white. 



KEY TO SPECIES 



Larvae 



1. Apex of frons bearing a pair of large, 



rounded lobes, fig. 179 



obscura, p. 51 



Apex of frons bearing smaller, pointed 

 lobes, figs. 180-182 2 



177 

 Larval Mandibles 



Fig. 173. — Dolophilus shawnee. 

 Fig. 174. — Trentonius distinctus. 

 Fig. 175. — Chimarra socia. 

 Fig. 176. — Chimarra feria. 

 Fig. 177. — Chimarra aterrima. 

 Fig. 178. — Chimarra obscura. 



178 



